Article formed of thermoplastic synthetic resins and process of manufacturing the same



March 18, 1941. a VERNON ETAL 2,234,994

ARTICLES FORMED 0F THERMOPLASTIC SYNTHETIC RESINS AND PROCESS OF MANUFACTURING THE SAME Filed lay 20, 1939 vilwd ATTORNEY Patented, Mar. is, 1941 V UNITED STATES.

2,234,994 ARTICLE roam or mamormsrro- SYNTHETIC BESINS AND PROCESS OF M'ANUFACTUBING: THE SAME Lester B. Vernon, Beaver, and Harold M. Vernon,

Thornbnrg, Pa, assignors to The Vernon- Benshoi! Company, Pittsburgh, Pa", a corporation of Pennsylvania Application May 20, 1939, Serial No. 274,840

7 Claims.

This application is a continuation in part oi! our patent application Serial No. 119,870, filed January 9,1937. l

Ourinvention relates to articles, such for inh stance as artificial dentures, which are formed of thermoplastic synthetic resins, and to the method of manufacturing the same. Although our invention is particularly adapted to the manufacture oi dentures, it also may be advantatd teously applied to the production of any article or object in connection with which coloration and surface characteristics are important considerations.

For the purposes which we have in view we yj employ synthetic resins of the thermoplastic type, which when polymerized are characterized by what we term an "elastic memory.

By thermoplastic resins is meant that class oi synthetic resinous compounds which soften when m heated-so as to be workable for shaping and torming purposes," but which do not undergo chemical changes at ithesoftening temperature. Examples of such resins are those derived from acrylic acid, such as methyl methacrylate, ethyl at methacrylate, vinyl chloride, vinyl acetate, and interpoiymers thereof. Doubtless there are many other resins possessing this property, but we have successfully used those above mentioned in the practice of our invention. gm Such resins when polymerized in any given shape, tend to retain such shape. When heated the shaped resin does not melt but becomes more yielding and rubbery and when sufllcient external pressure is applied it may be molded into gm another'shape which it will retain when cool.

Thus if the polymerized resin is in the form of a sphere and is then flattened under heat and pressure, itwill retain its flattened form unless reheated sumciently restore its rubbery state; when it will tend to reassume its original spherical shape. V

This property for convenience we term elastic memory.

in the accompanying drawingrthe steps of the y, process disclosed herein are set forth diagrammaltlcally,

in the practice of our invention we preferably employ thermoplastic resins which have been fully or substantially polymerized and which arein W the form of relatively small grains or particles. While we prefer that the resins be reduced to powder orsmall particles in the polymerizing process so that each grain, however small or large, is spherical in shape, any process may be an employed to reduce the'resin, to particles either the particle substance.

producing a moulded article.

during polymerization or after. Thus the po1y-- merized resins may be cut, ground, milled, shaved,

shredded or otherwise reduced mechanically, or

i be irregular as to sizt'es.v

These polymerized grains are pouredinto a mould or other shaper, and are subjected to sufficient heat. and pressure to distort and surface 15 weld them together into a solid non-porous whole having surfaces conforming to the mould cavity of the desired contour; and it will be found that the article produced is composed of a multitude of welded-together particles more or less deformed 20 by the pressure but each maintaining its identity and possessing the property of returning to its original form when reheated free from too great restraining external pressure.

The moulded article appears to the eye to be as homogeneous. That is, if properly moulded, it appears that the constituent particles have totally coalesced and fused into one. mass. But in reality there has not been a fluid coalescence of race adhesion of particle to particle. 'And since liquefaction has not taken place, each constituent particle has retained its individual identity. They will have been compressed, stretched, flattened or variously distorted as the fortuity of 3d mould outline and of external pressure was im- 7 posed upon them, hut each particle is still intact.v

as to its original mass and substance. Moreover,

it tends to return to its original shape it reheatedfree from a restraining external pressure. dc

Thus if such resins are polymerized in the form of heads of different colors and also transparent heads, and the intermingled heads are pressed with heat into a mould, an examination of the article produced, after it has cooled, will reveal t that it is composed ofthe individual beads each. retaining its identity and color or transparency, and practically retaining their relative positions, and, while 'firmly welded together, changed in shape only to the degree resulting from the com- '50 'presslve forces employed in the moulding operation.

The following examplevis given to illustrate the temperature and pressure requirements for There has been only surtil I A quantity of a polymerized resin having the property of elastic memory is placed in a mould and is heated to a temperature of from approximately 285 F. to 315 F. and subjected to a pres- 5 sure of 1500 to 5000 pounds per square inch.

The time required for producing the moulded article under these temperatures and pressures depends largely upon the particular resin and the character of thearticle being produced as 10. is well understood by those skilled in the art.

If a plasticizer is added to facilitate the moulding operation the temperatures and pressures required are reduced as isalso well known by those skilled in the art.

16 Now. if the surface, or a portion of the surface of the moulded article be subjected temporarily to enough heat to again make the resin rubbe y. the beads or particles in the affected surface area tend to resume the shapes they had 20 before pressing or the shapes into which they were originally polymerized. Thus, if the article was moulded of spherical grains, and then is heated again after removal'from'the mould, the whole, surface will become pebbly by reason of 25 the fact that the surface grains tend toround up in their former shapes again. Likewise if the resin put into the mould was a powder of very fine grains, the reheated surface will have the appearance of ground or etched glass;

80 In the case of articles moulded of polymerized particles of thermoplastic synthetic resin which has the property of elastic memory, the individual surface particles may be caused to reassume,

to a desired degree, their original shapes by the 35 application of localized heat; This heating may be accomplished in any convenient manner, such as by subjecting the surfaces or a selected portion 'of a surface or surfaces of the moulded article to dry heat, the heat of an open flame,

to a steam jet or atmosphere, or to contact with a heated implement. Again, the article may Q be immersedorpartlallyimknersedtoboilingwa- 55 colors noticeable upon close examination, and

, which aresynthetized by the eyeinto a more or less uniform coloration. v

Under the present practice in the manufacturing of artificial dentum the reproduction of m such colorconditlons has been-unattainable.

Again, it has long been recognized that natural oral tissue is not glassy or smooth like a polished surface but presents a slightly roughened, pebbly or ridged or rib-grained surface.

55 Denture manufacturers have attempted to imij tate this natural surface but with little success. They have tried stipplingthe wax base plate, and stippling or tooling the surface of the artiflcial denture, with very indifferent result.

7 This natural surface of the denture is not only of importance from the consideration of appearance, but also it is important for masticatory efficiency. In the palatal section of the human mouth and on the lingual surface of the alveolar 15 ridges the slightly pebbled, ridged orreticulated surface of the natural tissue aids in mastication and assists in forming a bolos of the food.

Thus in an artificial denture a surface as nearly as possible reproducing the natural surface of the oral tissue is desired not only for aesthetic reasons but also for practical purposes such as opposing a nrore nearly normal surface to the tongue.

In manufacturing an artificial denture in accordance with our invention, we mix the grains of polymerized resin of the necessary different colors, or colored grains mixed with transparent grains, or transparent grains, and fill the mass into the-mould, and then apply suflicient heat to cause them to assume a rubbery state and sumcient pressure to firmly compress them in the mould so that the particles become welded together and form a denture of the desired shape.

When cooled and removed from the mould the denture presents a close imitation of coloration 2 .of the human oral tissue.

Wemay apply heat to the surface of the denture, or to such portions of the same as may be desired, to raise the temperature of the particles oral tissue. Or, if no coloration is desired, we may employ transparent resin so that the color of the natural tissue shows through the denture.

If desired, a portion-only of the denture may be formed in accordance with our invention, suchportion being embedded in or otherwise attached to the body of the denture whichmay be made of other materials such for instance as resins not possesing the property of elastic memory.

By the use of our invention we are enabled not only to reproduce with great faithfulness the natural coloration of the human oral tissues but also to provide the desirable slightly pebbled,

ridged and reticulated sm'faces. It is obvious that the advantages of our inventionare not confined to artificial dentures,

but our invention may be employed in the pro-' duction of articles intended for many uses wherein coloration and surface characteristics of the general characters described may be desirable 5o for ornamental or utilitarian reasons.

We claim:

1. The process of finishing a surface of a moulded article formed of synthetic resin having the property of elastic memory which comprises --reheating the selected surface area or areas of surface conforming to the cavity of the mould.

removing the molded substance from the mold. and reheating a. surface of the moulded article I to a temperature suflicient to cause the individual surface particles to yeassume their o 81- nal'shape to the desired degree.

' 3. The process of producing articles of syn- J thetic resins having the property of elastic mem- 'ory, which comprises filling a mould with particles of polymerized resin having an elastic memory, the particles being selected in accordance with their individual coloration, applying heat and pressure thereto sufllcient to distort and surface weld the particles together into a solid nonporous whole conforming to the cavity of the mould, removing the molded substance from the mold, and reheating a surface of the moulded article to a temperature sufficient to cause the individual surface particles to reassume their original shape to the desired degree.

4. The process of producing articles of syn thetic resins having the property of elastic memory, which comprises filling a mould with particles of polymerized resin having an elastic memory, applying heat and pressure thereto suflicient to distort and surface weld the particles together into a solid non-porous whole having a surface conforming to the cavity of the mould, removing the molded substance from the mold, and reheating a surface of themoulded article to a temperature of between approximately from 140 F. to 240 F. to cause the individual surface particles to reassume their original shape to the desired degree.

5. The process of producing articles of synthetic resins having the property of elastic memcles of polymerized resin having an elastic memory, the particles being selected in accordance with their individual coloration, applying heat and pressure thereto sufficient to distort and surface weld the particles together into a solid nonporous whole conforming to the cavity of the mold, removing'the molded substance from the mold, and reheating a surface of the moulded the surface of the article present their original shape to a selected degree.

'7. A moulded article formed of variously colored particles of polymerized synthetic resin having the property of elastic memory, .which particles are distorted from their original shape and surface-welded together into a solid non-porous whole except that the exposed portion of the individual particles at the surface of the article present their original shapeio a selected degree.

LESTER- B. VERNON.

HAROLD M. VERNON. 

